In view of the characteristics of low aluminum, high silicon and high iron in a bauxite ore in Yunnan province, a high aluminum-silicon ratio aluminum concentrate was obtained by roasting-alkali leaching pre-desilication process. The effects of roasting temperature, roasting time, Na2O concentration, alkali leaching time and liquid-solid ratio on pre-desilication were investigated. Under the optimal pre-desilication conditions including roasting temperature of 1 050°C, roasting time of 30 minutes, concentration of leaching agent Na2O of 80 g/L, leaching time of 90 minutes, and liquid-solid ratio of L/S=8 mL/g, the Al-Si ratio of low-grade bauxite can be increased from 4. 08 to 17. 98, and the desilication rate is up to 77. 31%, the relative dissolution rate of alumina in pre-desilicated concentrate can reach 94. 56%, and the dissolution effect is ideal. Combined with thermogravimetric differential scanning calorimetry, X-ray diffraction analysis, infrared spectroscopy and other characterization methods, the mechanism of pre-desilication by roasting-alkali leaching was analyzed. The results show that improvement of the Al-Si ratio of bauxite is due to the fact that the kaolin-type silicate minerals in the raw ore can be first converted into alkali-soluble amorphous SiO2 by roasting, and the efficient separation of aluminum silicon can be achieved by atmospheric pressure alkaline leaching, and aluminum concentrate with high aluminumsilicon ratio can be obtained.